The Mn to Cr mass ratio in supernova ejecta has recently been proposed as a tracer of Type Ia SN
progenitor metallicity. We review the advantages and problems of this observable quantity, and
discuss them in the framework of two Galactic supernova remnants: the well known Tycho SNR
and W49B, an older object that has been tentatively classified as Type Ia. The fluxes of the Mn
and Cr Ka lines in the X-ray spectra of these SNRs observed by the Suzaku and ASCA satellites
suggest progenitors of supersolar metallicity for both objects.